As a trace gas detector for a gas chromatograph, detectors adopting various methods, such as a TCD (Thermal Conductive Detector) and an ECD(Electric Capture Detector), are being proposed and put to practical use, and a detector that is currently most generally used is an FID (Flame Ionization Detector). The FID achieves a wide dynamic range (about six figures) by ionizing sample gas by a hydrogen flame and measuring the ionization current.
Furthermore, a detector which generates an excited species of inert gas, such as He, N2, Ar, Ne or Xe, by plasma that is generated by high-voltage discharge, and which thereby ionizes a sample is proposed. For example, a PDD (Pulsed Discharge Detector) generates plasma by causing spark discharge by application of a pulsed high voltage. A method that uses plasma does not need hydrogen and generally, the ionization efficiency thereof is higher than that of the FID. For example, the ionization efficiency for propane is 0.0005% for the FID and 0.07% for the PDD.
With respect to generation of plasma by a method different from that of the PDD, there is a method that uses dielectric-barrier discharge (see Non-Patent Document 1). With the dielectric-barrier discharge, since the surface of an electrode for generating discharge is covered with a dielectric material, there is not much emission of thermal electrons, secondary electrons and the like that occur in the case of generating discharge by using metal electrodes, and the stability of plasma generation is high. Further, a discharge current is suppressed by the dielectric material, and thus, there are characteristics that deterioration of electrodes and heat generation at electrodes may be suppressed, and that the durability is high.
As the PDD or an ionization detector that uses dielectric-barrier discharge, there is one that performs ionization of a sample by mixing, in the sample, an excited species generated by plasma generated by discharge, and a discharge ionization current detector that performs ionization of a sample by excitation light that is emitted at the time of generation of plasma by discharge (see Patent Document 1, Non-Patent Document 2).